ABSTRACT: The hypothesis was proposed that shore fishes and crabs, predators other than gastropods, may be primarily responsible for depletion of barnacle populations in the vicinity of crevices through thigmotactic behaviour during foraging. To test this
hypothesis, movements of mobile predators on barnacle-dominated rock in the lower intertidal zone were observed using a fixed underwater television camera. An area of 0.2 m2 was monitored continuously for 14 d on a vertically oriented but
relatively protected shore on the west coast of Scotland. Infrared lights during nighttime high tides lit the area. Stereo photography was used to determine the topography of the area. The principal species seen by day was the blenny Lipophrys
pholis (L.) while the shore crab Carcinus maenas (L.) was the most frequent species at night. Scorpion fish Taurulus bubalis (Euphrasen), dogwhelks Nucella lapillus (L.) and a single North American
mink Mustela vison Schreber were also seen. Movements of crabs, and especially blennies, were concentrated around small-scale concavities in the rock surface of less than 10 cm dimensions, supporting the primary hypothesis. Times spent by
Lipophrys pholis and Carcinus maenas in 0.001 m2 (10 cm2) areas within the video frame varied by 3 and 2 orders of magnitude, respectively. These 2 species are known to be active predators of barnacles
Semibalanus balanoides and showed behaviour consistent with attacks on barnacles as prey. Observed movements and apparent spatial concentration of attacks, especially around crevices, may be a cause of patchiness in barnacle populations at
this scale.